Proposed Viability Criteria for Puget Sound Steelhead

Jeff Hard, Northwest Fisheries Science Center of NOAA Fisheries

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Puget Sound steelhead were listed as a threatened species under the Endangered Species Act in 2007. The Puget Sound Steelhead Technical Recovery Team (TRT) has proposed viability criteria for these fish to assist with recovery planning. The TRT developed an approach, based on the Viable Salmonid Populations (VSP) concept, for evaluating viability that considers abundance, productivity, genetic and phenotypic diversity, and spatial distribution as primary axes of steelhead persistence and sustainability. Abundance and productivity address the demographic health of a population, while diversity and spatial structure address its ability to persist and adapt to future challenges. The TRT has applied the framework hierarchically to demographically independent populations (DIPs), to groups of populations with similar characteristics (Major Population Groups, or MPGs), and to the protected conservation unit—the Distinct Population Segment, or DPS—as a whole.

The approach the TRT is proposing considers several types of information that influence key aspects of viability, including recent abundance relative to estimates of historical capacity, probability of reaching a low abundance threshold, population growth rate, changes in age structure and spawn timing, occupancy of suitable habitat by adults and juveniles, frequency of repeat spawning, and influence of hatchery fish. Some of these factors can influence more than one VSP parameter, but in different ways. For example, restricted spatial distribution can affect the demographic condition of a population but is also likely to influence the impact of future catastrophic events or the ability of a population to “bet hedge” by expressing multiple life-history strategies.

The information available for Puget Sound steelhead needed to assess viability in a comprehensive way varies substantially in quality and quantity. To accommodate this diversity of information, the TRT adopted a decision support system—an analytical tool that can help to guide transparent and supportable decisions when considerable uncertainty is inherent in the information. The system implements a hierarchical set of Bayesian networks that estimate the probabilities that different factors influence viability at the level of the DIP, MPG, and DPS. It can also readily accommodate new or improved information as it becomes available.

The TRT is using this system to both assess steelhead viability across Puget Sound and develop recommended biological criteria for viability. Importantly, the patterns of variation across the factors influencing viability can be used to construct simple decision guidelines to assess viability throughout the DPS and help to identify factors that may be limiting steelhead performance.

In this presentation, I will outline the TRT’s approach, use some simple examples to illustrate how it works, show how the tools can be used to characterize viability and inform strategies for recovery planning, and recommend viability criteria for Puget Sound steelhead.